When it comes to the roof of the building, then the word "bias" is meant the angle of the roof membrane to the horizon.In geodesy, this parameter is a measure of the steepness of the slope, and in the project documentation it is the degree of deviation from the basic elements of straight lines.The slope in degrees does not cause anybody problems, but the bias in percentage sometimes causes confusion.It is time to deal with this unit of measurement to be clear about what it is and, if necessary, easily translate it in other units, for example in the same degrees.
Calculation of percentage deviation
Try to right-angled triangle ABC, lying on one of its legs of AB.The second leg of the sun will be directed vertically upward and forms the hypotenuse of the AU with a lower angle of the leg.Now we have to think a little bit and trigonometry to calculate its tangent, which just characterizes the slope formed by the hypotenuse of a triangle with the bottom two sides.Assume that the cathetus AB = 100 mm and BC = 36.4 mm.Then the tangent of the angle of our equals 0.364, which corresponds to the tables 20˚.What, then, will be equal to the slope in percentage?To convert the value obtained in these units, we simply multiply the tangent 100 and get 36.4%.
How to understand the angle of the slope in percentage?
If a road sign shows 12%, it means that every kilometer of the ascent or descent the road will climb (descend) to 120 meters.To convert a percentage to degrees, you simply calculate the arc tangent of the value and, if necessary, transfer it from radians to degrees familiar.The same applies to the construction drawings.If, for example, indicates that the angle of slope in percent is 1, it means that the ratio of one to the other leg equals 0.01.
Why not in degrees?
Many certainly interested in the question: "Why use the slope for some other interests?" Indeed, why not do some degree.The fact that at any measurement always occurs some error.If the project documentation will be applied degrees, it will inevitably have difficulties with the installation.Get at least the same sewer.The error of a few degrees at a length of 4-5 meters can get her in a completely different position from the right side.Therefore, in the instructions and recommendations of the project documentation is usually applied interest.
Application in practice
assume that the project involves the construction of a country house unit pitched roof.Requires check its bias in percentage and degrees, if you know that the ridge height is 3.45 meters, and the width of the future home is 10 meters.Because the front roof is an equilateral triangle, it can be divided into two right triangles in which the height of the ridge will be one of the legs.The second leg we find dividing the width of the house in half.Now we have all the necessary data to calculate the slope.Get: atan-1 (0.345) ≈ 19˚.Accordingly, the bias is equal to 34.5 percent.What can we do for you?First, we can compare this value with the parameters recommended by experts, and secondly, to check with the requirements of SNIP when choosing a roofing material.Referring to the directories, you can find out what kind of tiles for laying a level slope is too small (minimum level equal to 33 degrees), but such a roof is not afraid of strong wind gusts.
